Multiple battery charger with automatic charge current adjustment

ABSTRACT

Systems and methods using the same to achieve a multiple battery charger with automatic charge current adjustment have been disclosed. The invention maintains equilibrium of charge levels during charge and discharge between all of the multiple batteries. For each battery a charger block comprising a unidirectional means and a current source for charging is assigned. The on-resistance of each charger block is automatically splitting the charge current available to the various batteries thus maintaining an equilibrium of charge levels of the batteries, i.e. supporting the battery with the lowest charge level with the highest charge current until equilibrium is reached.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates generally to charging of batteries and relatesmore specifically to multiple battery chargers having automatic chargecurrent adjustment.

(2) Description of the Prior Art

Battery powered small electronic devices such as mobile phones, personalmusic players; mobile computers are gaining more and more popularity.These devices need to be recharged quite often to remain functional.

Most battery charger circuits for portable devices with embedded ornon-frequently changed batteries support only one battery as shown below

FIG. 1 prior art shows a typical charger circuit 1 comprising a linearor switching converter 2 converting a charger supply voltage to aVDD_OUT voltage as required by a system load and by a battery charger 3charging a battery 4 with an output voltage VBAT. An output capacitor 5is smoothing the output voltage VDD_OUT.

This approach is limiting the system to only one battery, which doesrestrict the possibilities to design the shape of a handheld device asdesired by customers. Examples for such devices are mobile phones or MP3players

Multiple batteries can be charged for other portable devices. This isachieved by multiple charger blocks, which independently charge eachbattery. This also requires a separate charge current control and thesystem supply must be strong enough to support all battery currents inparallel as e.g. described by U.S. Pat. No. 5, 486,749 by Brainard.

In this case, the system voltage must always be high enough to chargeeach battery and in addition the delivered current out of the inputvoltage regulator needs to be higher as the maximum system load and thebattery currents to avoid, that the system supply will be crow bared.

As example FIG. 2 prior art shows such a system for charging multiplebattery cells 4 comprising a converter 2 converting from charger supplyto VDD_OUT voltage, a charge and discharge control unit 20, and for eachbattery cell 4 a charger 3. This control unit 20 decides which batteryis active and controls the charge of the active battery. Each batterycell 4 shown in FIG. 2 prior art has its own connection towards thesystem supply and the system can decide, which battery to use. It isalso possible to run the system with only one of the batteries.

There are known patents dealing with the charging of multiple batteries:

U.S. patent (U.S. Pat. No. 6,768,286 to Trembley) proposes a batterycharger method and apparatus for providing detailed battery status andcharging method information for a selected one of multiple batteriesthat are simultaneously coupled to the battery charger. The batterycharger includes a controller. The controller selects one of thebatteries to monitor and charge. The controller then starts ameasurement cycle for the selected battery. During the measurementcycle, the controller determines current battery characteristics of theselected battery. The controller determines whether the selected batteryis ready for charging by determining whether the battery characteristicsof the selected battery are within a specified range. If the controllerdetermines that the selected battery is ready for charging, thecontroller causes the battery charger to start charging the battery. Ifthe controller determines that the selected battery is not ready forcharging, the controller selects another battery to monitor and charge.Detailed information about the selected battery may be provided from thecontroller to a processor that is external to the controller.

U.S. patent (U.S. Pat. No. 6,456,044 to Darmawaskita) discloses a singleintegrated circuit package for controlling the charging circuits of abattery charger. The single integrated circuit package comprises amicrocontroller, switch mode power supply controller(s), analog todigital converter and analog input multiplexer which may be fabricatedon a single integrated circuit die, or the microcontroller may be on oneintegrated circuit die, and the remaining aforementioned circuits may beon a second integrated circuit die. The switch mode power supplycontroller is adapted for connection to a power converter, which is usedto control the voltage and/or current to a battery being charged. Thepower converter may also be on the same integrated circuit die as theswitch mode power supply controller, or may be on a separatesemiconductor die but included in the single integrated circuit package.Single or multiple batteries may be charged using charging algorithmsspecifically tailored to each battery. Batteries being charged may havea different capacity, voltage, or chemistry type. State of charge andtime to reach a fully charged condition for each battery may also bedifferent.

U.S. Pat. No. (U.S. Pat. No. 6,445,159 to Ramsden) describes a circuitfor charging multiple batteries simultaneously. The circuit monitors theamount of current being delivered to a first battery and compares it toa maximum available current. The circuit then delivers the difference toat least a second battery. The circuit includes a current sensingresistor and comparator for actuating a series switch to electricallycouple and decouple a second battery depending upon the demands of thefirst battery. An optional microprocessor can manipulate a referencethreshold to allow simultaneous charging of multiple batteries. Theinvention greatly reduces the time needed to charge a primary and sparebattery.

U.S. patent (U.S. Pat. No. 5,486,749 to Brainard) discloses a batterycharging system that includes an efficient switch mode power supply,multiple linear current limiters, and feedback means to allow the switchmode power supply to operate at the minimum voltage necessary to operatea power load and charge batteries. Furthermore, the switch mode powersupply is capable of producing the maximum power required by the system,such as when the battery charger is used in conjunction with operationof an electronic device with peak load demands such as when a hard diskis accessed in a portable computer. Two control mechanisms are found inthe battery charging system. The first mechanism is an input used tocontrol the switch mode power supply output voltage from an externalsource. In one embodiment, this is done by referencing a first voltageto that internal to the switch mode power supply. The second mechanismis to limit the current within the switch mode power supply notcontrolled by an external source. This current limiting feature islinear and is set at an absolute limit point. Each limiter suppliescharge current to a battery, which charge current is monitored andcompared to a reference voltage with the resulting error voltage used tocontrol the output of a series pass controller, such as a transistor.

It should be understood that Brainard discloses a charge mode ofmultiple battery cells in parallel. Each battery requires its owncontrol unit and most important the provided current must be higher asthe required current.

U.S. patent (U.S. Pat. No. 6,081,096 to Barkat et al.) discloses adevice including detachable main and auxiliary batteries and a circuitfor discharging and charging the batteries. Two batteries are charged insequence. Discharging is accomplished by an auxiliary switch thatconnects the auxiliary battery to power the device, a detector, and amain switch that connects the main battery to power the device, withoutinterruption, when the auxiliary battery drops below a predeterminedvoltage as determined by a detector. Charging is performed by switches,an internal charger, and a controller. When both batteries are attached,the controller uses the switches to select and couple charging currentgenerated by the internal charger to the main battery. Once charged, thecontroller switches to charge the auxiliary battery.

U. K. Patent (GB 224 2794 to Ashworth) teaches an apparatus for charginga main NiCd battery B1 in a portable electronic apparatus, specificallya cellular radio telephone, and also a spare NiCd battery B2 first fastcharges battery B1 until a predetermined charge state is reached, whereafter battery B2 is fast charged until it reaches the predeterminedcharge state. Both batteries B1 and B2 are charged according to apriority sequence. Battery B1 is then trickle charged until thetelephone is removed from the apparatus, whereupon battery B2 is tricklecharged. The apparatus may have a base unit into which the telephone andbattery B2 can be plugged, and a charging current supply separablycoupled to base by connectors so that the supply can also be used on itsown.

SUMMARY OF THE INVENTION

A principal object of the present invention is to achieve methods andsystems to achieve a charger of multiple batteries with automaticcurrent adjustment

A further object of the present invention is to achieve a chargermaintaining equilibrium of charge levels between multiple batteriesduring charge and discharge.

A further object of the present invention is to achieve an automaticcontrol method for multiple battery charging

Another further object of the present invention is to achieveself-balancing of the charge currents of multiple batteries wherein theon-resistance of multiple charger blocks is naturally splitting theavailable charge to various batteries.

In accordance with the objects of this invention a method to chargemultiple batteries of a mobile electronic device by automaticallybalancing charge and discharge of each battery has been achieved. Themethod invented comprises, firstly, the following steps: (1) providing asystem supplying current to a system load of a electronic mobile deviceand charging multiple batteries comprising a voltage converter, avoltage comparator, and a charge block for each battery to be charged,(2) connecting said system to a charger supply, and (3) comparing,initially only, right after connecting the system to a charger supply,if voltages of one or more batteries are well above voltages of otherbatteries and, if so, go to step (4), else go to step (5). The nextsteps of the method are (4) balancing the charge level of the batterieswithout supplying charge current from the voltage converter until thecharge levels of all batteries are the same, and (5) charging thebatteries by a charge current from the voltage converter byself-balancing the charge current for each battery by naturallysplitting the available charge current depending upon the on-resistancesof each charger block in order get a same charge level for each battery.The last steps of the method are (6) checking, if all batteries arefully charged and, if so, go to step (7) else go to step (5), and (7)discontinue charging the batteries and provide current required for thesystem load by voltage converter until voltage converter is plugged-off.

In accordance with the objects of this invention a system for chargingany number N multiple batteries of a mobile electronic device byautomatically balancing charge and discharge of each battery has beenachieved, The system invented comprises, firstly a voltage converterreceiving a charger supply voltage and providing a DC voltage asrequired by the electronic device, and a voltage comparator comparing,only initially after plug-in of the charger supply voltage, an actualoutput voltage of the voltage converter with an expected output voltageof the converter, and issuing a wait signal to N charger blocks, if theactual output voltage of the system is higher than the initiallyexpected output voltage of the converter. Furthermore the systemcomprises said N charger blocks, wherein each of the charger blocks isconnected to a first terminal of a correspondent battery, each chargerblock comprising an unidirectional means to allow one or more abatteries to deliver current to the electronic device and to otherbatteries, and a means of current source to provide a charge current tothe correspondent battery.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of thisdescription, there is shown:

FIG. 1 prior art shows a typical charger circuit charging one singlebattery cell.

FIG. 2 prior art shows such a system for charging multiple batterycells.

FIG. 3 shows a block diagram of the multiple battery charger invented.

FIG. 4 illustrates how the self-balancing of the present invention worksin case the battery voltage V_(BAT1) of the first battery is close tothe battery voltage V_(BAT2) of the second battery.

FIG. 5 illustrates how the self-balancing of the present invention worksin case the battery voltage V_(BAT1) of the first battery is well abovethe battery voltage V_(BAT2) of the second battery.

FIG. 6 illustrates a flowchart of a method invented for a rotation-basedfirst order noise-shaping DEM technique for use with 3-level DAC unitelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments disclose methods and systems for a batterycharger circuit to support multiple parallel batteries automatically andtreating them similar to a single battery after the batteries did reachequilibrium—which is done automatically. This means, that after aninitialization phase, which will start automatically after inserting abattery, the system is charging the parallel batteries the same way as asingle battery.

A key advantage of the present invention is that an automatic regulationscheme does not need any software or user interaction. Furthermore itsupports different charging states of batteries and automaticallybalances charge and discharge form each battery and does automaticallyadjust when connected first.

The charger block (active diode and linear charger block and connectionto the End-of-Charge (EOC) DAC can be implemented instantaneouslymultiple times. This solution does therefore support charging anddischarging any number of batteries without restriction.

The regulation concept invented does not need special user interaction.It can cope with different type of batteries and initial charge level.The regulation will self adjust the output voltages of the batteriesafter first connection. The self-balancing does occur during charge anddischarge mode automatically.

FIG. 3 shows a block diagram of the multiple battery charger invented.It comprises a converter 30 converting a charger input voltage toVDD_OUT voltage supporting a system load of an electronic device. Theconverter 30 could be a linear converter or a switching converter.Alternatively the converter 30 could be an AC-DC converter also.

A charger block 31 is provided for each battery 4 to be charged. Eachcharger block comprises an active diode 33 and a linear charger 34.

Via the active diode 33 or any other unidirectional means of thecorrespondent charger block 31 a correspondent battery 4, having abattery voltage higher than VDD_OUT, can provide the current requiredfor the system load or for charging other batteries having a lowercharge level. As it is known in the art an active diode is a circuitwhich can generally be directly substituted for an ordinary diode butwith improved characteristics, as e.g. a reduced the diode forwardvoltage drop.

In a preferred embodiment of the invention switching charger 34 provideconstant-current/constant-voltage charging. The charging current can beuser set and can be sensed internally. Other types of chargers could bealternatively deployed as well, such as e.g. linear chargers.

Optional resistors 32 or other means of resistance between the batteriescan be deployed to achieve equilibrium during discharge.

It should be noted that a charge and discharge control block 20, whichis constantly controlling the charge currents, as shown in FIG. 2 priorart is not required with the present invention.

In a preferred embodiment of the present invention VDD_OUT voltage isregulated initially by the converter 30 to Vbatmin plus a “safetyvoltage” of e.g. 0.2 V as the minimum supply. Vbatmin is the minimumvoltage required by the system.

The initial regulation is setting the voltage a little bit higher thanVbatmin, this “safety voltage” of 0.2 V mentioned above could also bee.g. 0.15 V or 0.25 V or in the order of magnitude of about 5-7% higheras Vbatmin as well. Different percentages are also possible. Thisapproach does always charge the lowest battery with the highest chargecurrent and batteries with higher voltages do join in later depending ontheir charge status.

This regulation concept allows the self-balancing of the charge currentsdepending on the charge state of each individual battery. This meansthat the ON-resistance of each charger block is naturally splitting theavailable charge current from the converter 30 to the various batteries.In order to achieve an equilibrium of charge levels by self-balancingthe batteries the regulation of the present invention provides thehighest charge current to the battery with the lowest level of chargeuntil equilibrium charge levels has been reached.

This concept is especially suited for application of switching chargers34 in the charging blocks 31, because the conversion of the chargersupply to VDDOUT adjustment to the lowest battery voltage, as e.g.Vbatmin+e.g. 0.2 V, improves the overall efficiency of the chargersystem.

FIG. 4 illustrates how in the self-balancing of the present inventionworks, i.e. FIG. 4 represents a situation wherein a battery voltageV_(BAT1) of a first battery is close to a battery voltage V_(BAT2) of asecond battery. In order to avoid unnecessary complexity FIG. 4 shows anexample of two batteries only, it has to be understood that more thantwo batteries can be supported by the present invention the same way aswell.

FIG. 4 shows the output voltage of the charger circuit V_(DD) _(—)_(OUT), the battery voltage V_(BAT1) of a first battery, a chargecurrent I_(BAT1) of the first battery, the battery voltage V_(BAT2) of asecond battery, and a charge current I_(BAT2) of the first battery. FIG.4 illustrates a case wherein the voltages of both batteries are closetogether.

At the point of time t₀ the charger unit is plugged in, V_(DD) _(—)_(OUT) rises to an initial voltage of e.g. 3.6 V, the first battery hasa voltage VBAT_1 of below 3.4 V and the second battery has a voltageVBAT_2 higher than 3.5 V, e.g. 3.6 V. The invention is of course notlimited to these voltages of 3.6 V, 3.5 V, or 3.4 V. These are typicalexamples only.

Since initially the voltage V_(BAT1) is lower than V_(BAT2), only thefirst battery is charged, hence I_(BAT1) rises in two steps, whileI_(BAT2) remains low and subsequently V_(BAT1) rises until V_(BAT1)equals V_(BAT2) at the point of time t₁ indicated by the vertical dottedline in FIG. 4. As soon as V_(BAT1) equals V_(BAT2) the charging currentI_(BAT2) rises also charging the second battery. Both batteries arefully charged at point of time b and equilibrium of charge levels, i.e.battery voltages, is reached. Hence both charge currents I_(BAT1) andI_(BAT2) fall back to zero.

If one of the batteries is well above, e.g. 100 mV, the lowest battery,the automatic regulation concept does first balance the battery chargestatus and the charger circuit is put into a wait condition. As soon asthe balancing did occur, the VDD_OUT voltage regulation does start towork and begins to charge as described in the case illustrated in FIG.4. It should be noted that, whenever there are different voltages of thebatteries, the batteries must balance the charge status independently ofthe absolute voltage.

FIG. 5 illustrates how the self-balancing of the present invention worksin case the battery voltage V_(BAT1) of the first battery is well abovethe battery voltage V_(BAT2) of the second battery. FIG. 5 shows theoutput voltage of the charger circuit V_(DD) _(—) _(OUT), a WAIT signal,the battery voltage V_(BAT1) of a first battery, a charge currentI_(BAT1) of the first battery, the battery voltage V_(BAT2) of a secondbattery, and a charge current I_(BAT2) of the first battery.

In case one of the batteries is well above the lowest battery, theautomatic regulation concept does first balance the battery chargestatus and the charger circuit is put into a wait condition. As soon asthe balancing has been performed at t1, the VDD_OUT voltage regulatordoes start to work and begins to charge as described in case 1. In anexample of a preferred embodiment “well above” means a difference in theorder of magnitude of greater than 100 mV, “close to” means a differencein the order of magnitude of less than 100 mV. These definitions candiffer according to specific requirements of the charger systeminvented.

The VDD_OUT voltage converter 3 detects the wait condition by acomparison of the output voltage of the batteries. Alternatively theVDD_OUT voltage regulator detects the wait condition by a comparison ofthe expected output voltage and the actual output voltage of VDD_OUT″

This is possible, because the highest battery (if above VBAT×min+0.2)does overdrive the VDD_OUT node via its active diode circuitryautomatically between to and The wait period is finished if thebatteries are close together, e.g. in the order of magnitude of 100 mV.

This Wait-condition is only happening with completely different batterycharge status and only at the very beginning. Still the system doesallow full operation even under that special condition.

It should be noted that a VDD_OUT comparator is the only additionalcontrol part of the charger unit, which has to be instantiated one timeonly. All other blocks are fully scalable.

Referring to FIG. 5, during a time frame before a plug-in of the chargerat t₀, the current required by a system load is provided by the firstbattery because VBAT1 is high enough to support the system load. Also aresistive balancing of the voltages of VBAT1 and VBAT2 starts via theoptional resistors 32 shown in FIG. 3. Balancing is performed bydischarging the battery with the highest battery voltage.

A wait signal is issued by the comparator as soon as the charger unithas been plugged-in because the actual VDD_OUT voltage is higher thanthe initially expected output voltage of the converter. During the waitphase between t₀ and t₁ an active balancing between the first and secondbattery is performed, the charge level of the first battery isdecreasing and the charge level of the second battery is increasingaccordingly, because energy of the first battery is transferred to thesecond battery. During the wait period current IBAT2, charging thesecond battery, is provided by the first battery, therefore currentIBAT1 is negative in FIG. 5. It should be noted that, in case the secondbattery is empty, equilibrium between both batteries is establishedfirst and then charging of the batteries starts. In case charging of thesecond battery would start at once equilibrium between the batteries maybe lost.

Optionally resistive balancing can be used as shown in a first phase ofFIG. 5. This is only possible if the optional resistors 32 and 42,indicated in FIG. 3, are deployed. During the resistive balancing thebattery voltages are coming closer together via the resistors 32 and 42.At point of time t₀ the charger supply is plugged in. During the waitingperiod between t₀ and t₁ an equilibrium between the voltages of bothbatteries is established by an active balancing, i.e. charging thesecond battery BAT_2 by IBAT_1. In the following period both batteriesare in equilibrium, i.e. having a same charge. Starting to chargebattery BAT_2 right away without a preceding balancing period would leadto a complete unbalanced system.

At the end of the wait period at time t₁ the charge status of bothbatteries is balanced and both batteries are charged by the currentsIBAT1 and IBAT2 until they are fully charged, e.g. to 4.2 V. During thischarging period VDD_OUT voltage rises also accordingly.

In regard of discharge of the batteries every portable system benefitsfrom low ohmic connection of the batteries to the load. This parallelbattery concept reduces the resistance between battery and load due tothe multiple active diode circuits. As each battery will self dischargewith different time constants, this system allows to align all chargelevels of the batteries using an optional resistor or any kind of ohmicconnection in between each of the batteries.

FIG. 6 illustrates a flowchart of a method invented to charge multiplebatteries of a mobile electronic device by automatically balancingcharge and discharge for each battery. A first step 60 describes theprovision of a system supplying current to a system load of anelectronic mobile device and charging multiple batteries comprising avoltage converter, a voltage comparator, and a charge block for eachbattery to be charged. The next step 61 illustrates connecting thesystem to a charger supply voltage. The following step 62 describescomparing initially only, right after connecting the system to a chargersupply, if voltages of one or more batteries are well above voltages ofother batteries and, if so, go to step 63, else go to step 64. Step 63describes balancing the charge level of the batteries without supplyingcharge current from the voltage converter until the charge levels of allbatteries are the same. In step 64 the batteries are charged by a chargecurrent from the voltage converter by self-balancing the charge currentfor each battery by naturally splitting the available charge currentdepending upon the on-resistances of each charger block in order get asame charge level for each battery. The last step 65 describes checkingif all batteries are fully charged and, if so, go to step 67, else go tostep 64. Step 67 illustrates discontinuing charging the batteries andproviding current for system load by voltage converter until voltageconverter is plugged-off and system load is supported by the batteries.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1. A method to charge multiple batteries of a mobile electronic deviceby automatically balancing charge and discharge of each batterycomprising the following steps: (1) providing a system supplying currentto a system load of an electronic mobile device and charging multiplebatteries comprising a voltage converter, a voltage comparator, and acharge block for each battery to be charged; (2) connecting said systemto a charger supply; (3) comparing, initially only, right afterconnecting the system to a charger supply, if voltages of one or morebatteries are well above voltages of other batteries and, if so, go tostep (4), else go to step (5); (4) balancing the charge level of thebatteries without supplying charge current from the voltage converteruntil the charge levels of all batteries are the same; (5) charging thebatteries by a charge current from the voltage converter byself-balancing the charge current for each battery by naturallysplitting the available charge current depending upon the on-resistancesof each charger block in order get a same charge level for each battery;(6) checking, if all batteries are fully charged and, if so, go to step(7) else go to step (5); and (7) discontinue charging the batteries andprovide current required for the system load by voltage converter untilvoltage converter is plugged-off.
 2. The method of claim 1 wherein saidbalancing the charge level of the batteries without supplying chargecurrent is initiated by a wait signal;
 3. The method of claim 1 whereinsaid wait signal is set according to a comparison of the voltages of thebatteries.
 4. The method of claim 1 wherein said wait signal is setaccording to a comparison of the expected output voltage with the actualoutput voltage.
 5. The method of claim 1 wherein said balancing thecharge level of the batteries without supplying charge current from thevoltage converter is performed until the voltage levels of all batteriesare within a range in the order of magnitude of 100 mV.
 6. The method ofclaim 1 wherein each battery has its own connection the system load andto the output of said converter.
 7. The method of claim 1 wherein saidsystem load can be supported by only one battery.
 8. The method of claim1 wherein the method for charging multiple batteries does not need anysoftware
 9. The method of claim 1 wherein the method for chargingmultiple batteries can be applied for any number of batteries.
 10. Themethod of claim 1 wherein the output voltage of said voltage is set tois a minimum voltage required by the system plus a safety voltage ofabout 6 percent of said minimum voltage.
 11. The method of claim 1wherein said system load can operate also during said balancing of thecharge level of the batteries without supplying charge current
 12. Themethod of claim 1 wherein an initialization phase starts automaticallyafter inserting a battery,
 13. A system for charging any number Nmultiple batteries of a mobile electronic device by automaticallybalancing charge and discharge of each battery, comprises: a voltageconverter receiving a charger supply voltage and providing a DC voltageas required by the electronic device; a voltage comparator comparing,only initially after plug-in of the charger supply voltage, an actualoutput voltage of the voltage converter with an expected output voltageof the converter, and issuing a wait signal to N charger blocks if theactual output voltage of the system is higher than the initiallyexpected output voltage of the converter; and said N charger blocks,wherein each of the charger blocks is connected to a first terminal of acorrespondent battery, each comprising: an unidirectional means to allowone or more a batteries to deliver current to the electronic device andto other batteries; and a means of current source to provide a chargecurrent to the correspondent battery.
 14. The system of claim 13 whereinsaid voltage converter is a linear converter.
 15. The system of claim 13wherein said voltage converter is a switched converter.
 16. The systemof claim 13 wherein said unidirectional means is a diode.
 17. The systemof claim 13 wherein said unidirectional means is an active diodecircuit.
 18. The system of claim 13 wherein said means of current sourceis a linear charger circuit.
 19. The system of claim 13 wherein saidmeans of current source is a switched charger circuit.